Apparatus and method for forming single crystalline nitride substrate using hydride vapor phase epitaxy and laser beam

ABSTRACT

The present invention relates to an apparatus and a method for forming a single crystalline nitride substrate, and more particularly, to an apparatus and a method for preventing cracks from being generated in a single crystalline nitride substrate. A method for forming a compound semiconductor substrate includes the steps of: a) preparing a parent substrate; b) forming a single crystalline film on the parent substrate in a reacting chamber; c) maintaining the single crystalline film in a predetermined temperature which is higher than a room temperature; and d) illuminating laser beam on a backside of the parent substrate and separating the single crystalline film from the parent substrate. Accordingly, the present invention provides a large single crystalline nitride substrate, by preventing cracks caused by the lattice mismatch with the parent substrate.

TECHNICAL FIELD

The present invention relates to an apparatus and a method for making asingle crystalline nitride substrate; and, more particularly, to anapparatus and a method for preventing cracks from being generated in asingle crystalline nitride substrate.

BACKGROUND ART

A GaN single crystalline substrate, as an example of a singlecrystalline nitride substrate, will be described. Generally, the GaNmaterials has a melting point more than of 2400 and the dissociationpressure of nitride in the GaN materials is about ten thousandatmospheres. Accordingly, this high melting point and high dissociationpressure make it impossible to create a large single crystalline GaNbulk using typical growing methods of the semiconductor crystals. Aneedle-shaped crystal growing method, in which a gallium gas directlyreacts on an ammonia gas at a high temperature of about 1000° C. to1150° C., and a plate-shaped crystal growing method, in which nitrogenis dissolved in liquid gallium at a high temperature of about 1500° C.to 1600° C. and at a high nitrogen pressure corresponding to about 20000atmospheres has been used to create a single crystalline GaN bulk(hereinafter, referred to as a GaN bulk).

However, these crystal growth methods have made a small-sized GaN bulkwhich has only a few millimeters in size and about 100μm in thickness.Accordingly, it is impossible to achieve a commercial success in usingthe GaN bulk.

To solve the above problem, a hydride vapor phase epitaxy has been usedto create the GaN bulk at a growing rate of 100μm/hour. That is, afterforming a thick GaN film on a parent substrate, such as sapphire or SiCsubstrate, the parent substrate is removed and then the GaN bulk isfinally formed.

The removal of the parent substrate is carried out by the mechanicalpolishing method or laser beam. In particular to laser, as shown in FIG.1, after forming the thick GaN film on the parent substrate at a hightemperature of about 1000° C. to 1100° C., the thick GaN film on theparent substrate is cooled down to a room temperature. After increasingthe temperature of the parent substrate up to about 600° C., the thickGaN film is separated from the parent substrate using laser beam in anadditional apparatus different from the hydride vapor phase epitaxy(“Large free-standing GaN substrate by hydride vapor phase epitaxy andlaser induced lift-off,” by K. Kelly et al, Jpn. J. Appl. Phys. Vol. 38,No. 3A (pt 2), 1999).

In the above-mentioned hydride vapor phase epitaxy, since the thick GaNfilm is formed on the sapphire substrate at a high temperature and it iscooled down to the room temperature, cracks are generated by the latticemismatch and thermal expansion coefficients between the GaN film and thesapphire substrate. Because of these cracks, the GaN bulk is restrictedwithin a small-sized substrate and electric characteristics therein arealso deteriorated.

DISCLOSURE OF INVENTION

It is, therefore, an object of the present invention to provide anapparatus and a method for preventing cracks from being generated in asingle crystalline nitride substrate which is made by a hydride vaporphase epitaxy method.

Another object of the present invention is to provide an apparatus and amethod for forming a large single crystalline nitride substrate on acommercial basis.

In accordance with an aspect of the present invention, there is providedan apparatus for forming a compound semiconductor substrate, theapparatus comprising: a reacting chamber for forming a singlecrystalline film on a parent substrate; a heating chamber connected tothe reacting chamber within a processing channel, wherein the singlecrystalline film is separated from the parent substrate at a highertemperature than a room temperature; and a supporter for supporting thesingle crystalline film and the parent substrate and maintaining thesingle crystalline film in a predetermined temperature.

In accordance with another aspect of the present invention, there isprovided a method for forming a compound semiconductor substrate, themethod comprising the steps of: a) preparing a parent substrate; b)forming a single crystalline film on the parent substrate in a reactingchamber; c) maintaining the single crystalline film in a predeterminedtemperature which is higher than a room temperature; and d) illuminatinglaser beam on a backside of the parent substrate and separating thesingle crystalline film from the parent substrate.

According to the present invention, a thick GaN film is formed on aparent substrate, such as sapphire (Al₂ 0 ₃), spinel (MgAl₂O₄) orsilicon carbide (SiC), which has the lattice mismatch with the singlecrystalline GaN film and a different thermal expansion coefficient, andthe parent substrate is heated up to a range of 600° C. to 1000° C. Inthis temperature range, the single crystalline GaN film is separatedfrom the parent substrate by laser beam.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plot illustrating a temperature variation in a conventionalmethod for forming a single crystalline nitride substrate;

FIG. 2 is a plot illustrating a temperature variation in a method forforming a single crystalline nitride substrate according to the presentinvention;

FIG. 3 is a schematic cross-sectional view of an apparatus for forming asingle crystalline nitride substrate according to the present invention;and

FIGS. 4A to 4D are schematic cross-sectional views illustrating a methodfor forming a single crystalline nitride substrate according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 3, a horizontal type hydride vapor phase epitaxyapparatus of an atmospheric pressure is shown in order to form a singlecrystalline nitride substrate. The hydride vapor phase epitaxy apparatusincludes a reacting chamber 11A in which a quartz boat (not shown), isplaced, a heating chamber 11C having a supporter 40 to maintain aspecimen, and an exhausting chamber 11B positioned between the reactingchamber 11A and the heating chamber 11C and coupled to an exhaustingsystem 16. The temperature of the supporter 40 in the heating chamber11C is maintained in a specific temperature range and laser beamillumination to separate a single crystalline nitride film from a parentsubstrate 30 is carried out in the heating chamber 11C. Further, each ofthe chambers 11A to 11C adjacent to the exhausting chamber 11B is sealedup with shutters 12 and flanges 12A are mounted on both ends of thechambers 11A and 11C. Conventional mechanisms may be used to positionand move specimens and quartz boats in the chambers.

The reacting chamber 11A is surrounded by a multi-step electric furnace13 and is connected to a first inlet 14 to supply an ammonia gas and asecond inlet 15 to supply hydrochloric acid and nitrogen gases. Thesegases react on Ga materials 20 within the reacting chamber 11A and thena thick GaN film is deposited on the parent substrate 30 adjacent to theGa materials 20. While the thick GaN film is grown in the reactingchamber 11A, the reacting gases are purged away through the exhaustingsystem 16 in the exhausting chamber 11B and when the growth of thesingle crystalline nitride substrate (the think GaN film) has beenfinished, the reacting chamber 11A is isolated from the exhaustingchamber 11B by the shatter 12. The parent substrate 30 on which thethick GaN film is formed is removed onto the supporter 40 in the heatingchamber 11C without being exposing to air and laser beam is illuminatedon the backside of the parent substrate 30 at a temperature of about600° C. to 1000° C. to separate a single crystalline GaN film (think GaNfilm) from the parent substrate 30. It should be noted that the thickGaN film and the parent substrate 30 are not cooled down to a roomtemperature.

Although the exhausting chamber 11B, as shown in FIG. 3, is positionedbetween the reacting chamber 11A and the heating chamber 11C, thereacting chamber 11A may be adjacent to the heating chamber 11C and theexhausting system 16 may be directly connected to the reacting chamber11A.

The hydride vapor phase epitaxy apparatus shown in FIG. 3 may be used toform group III-N (nitrogen) compounds of single crystalline substrates,such as AlN, InN, GaInN, AlInN and AlGaInN, as well as the GaN singlecrystalline substrate, containers having Ga and In materials may beprovided in the reacting chamber 11A and the hydrochloric acid andnitrogen gases flow into the reacting chamber 11A. FIGS. 4A to 4Dillustrate a method for forming the GaN single crystalline substrate.

First, referring to FIG. 4A, the parent substrate 30 selected from oneof an oxide substrate, such as sapphire (Al₂ 0 ₃) or spinel (MgAl₂ O₄),and a silicon carbide substrate, such as SiC, is prepared and generallythese parent substrates may have the lattice mismatch with the GaNmaterials and a different thermal expansion coefficient.

Next, referring to FIG. 4B, the thick GaN film 31 is formed on theparent substrate 30 in the hydride vapor phase epitaxy apparatus, asshown in FIG. 3, having the quartz boat in its reacting chamber 11A andthe supporter 40 in its heating chamber 11C. The group III elements suchas Ga are positioned at a region which is maintained at a temperature ofabout 600° C. to 900° C. by the multi-step electric furnace 13. At thistime, the parent substrate is maintained at a temperature of about 1000°C. to 1100° C. The reacting chamber 11A in which the quartz boat isplaced is pumped out up to about 10-3 torr, the reacting chamber 11A isgradually heated, and then the nitrogen gas injection into the reactingchamber 11A starts from about 600° C. When the reacting chamber 11Areaches to a temperature at which the thick GaN film is to be grown, thehydrochloric acid gas flows onto the Ga materials in the quartz boat andthe ammonia gas is provided to the parent substrate 30 to form the thickGaN film 31 on the parent substrate 30 at a thickness of about 100μm to550μm.

After forming the thick GaN film 31 on the parent substrate 30, thesupply of the hydrochloric acid gas is broken off and the parentsubstrate 30 on which the thick GaN film 31 is formed is cooled with thesupply of nitrogen and the ammonia gases until the temperature of thethick GaN film 31 reaches to a predetermined temperature range, e.g.,about 600° C. to 1000° C.

Referring to FIG. 4C, when the temperature of the reacting chamber 11Areaches to 600° C. to 1000° C., the parent substrate 30 on which thethick GaN film 31 is formed is moved into the supporter 40 in theheating chamber 11C. At this time, the temperature of supporter 40 ismaintained at about 600° C. to 1000° C. and the bottom of the parentsubstrate 30 is turned over top so that the thick GaN film 31 isdirectly on the supporter 40. The turned upside of the parent substrate30 is illuminated by laser beam (50). It should be noted that the thickGaN film 331 and the parent substrate 30 are not cooled down to a roomtemperature.

Referring to FIG. 4D, the parent substrate 30 is separated from thethick GaN film 31 by the high power laser beam. Nd:YAG laser beam, whichhas wavelength of 355 nm, power of about 500 mJ, pulse period of 10 to20 Hz and pulse width of 5 to 6 ns, may be used. When this high powerlaser beam is illuminated on the parent substrate 30, the beam passesthrough the parent substrate 30 and is absorbed into the thick GaN film31. If the thick GaN film 31 absorbs the high power laser beam, the GaNmaterial, which is in a range of a few micrometers in thickness(dissolution area 32), are dissolved into gallium and nitrogen and thethick GaN film 31 is separated from the parent substrate 30 by thisdissolution of the thick GaN film 31.

Since the single crystalline GaN substrate (the separated thick GaN film31A has an uneven surface, the mechanical and chemical polishing using adiamond slurry is applied to the single crystalline GaN substrate 31A.

As apparent from the above, the present invention provides a highgrowing rate of the single crystalline nitride substrate without crackscaused by the lattice mismatch between other materials, by using thehydride vapor phase epitaxy method. Furthermore, the present inventionprovides stability and reliability of processing by effectivelyseparating the single crystalline nitride substrate from the parentsubstrate by laser beam.

Although the preferred embodiments of the invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

What is claimed is:
 1. A method for forming a nitrogen compoundsemiconductor substrate, the method comprising the steps of: a)preparing a parent substrate; b) forming a single crystalline nitridefilm on the parent substrate in a reacting chamber; c) moving the parentsubstrate on which the single crystalline nitride film is formed into aheating chamber that is connected to the reacting; d) moving onto asupporter the parent substrate, wherein the supporter is positioned inthe heating chamber; e) heating the parent substrate up to apredetermined temperature which is higher than a room temperature; andf) while the single crystalline nitride film is at about thepredetermined temperature that is higher than the room temperature,illuminating a laser beam on a backside of the parent substrate andseparating the single crystalline nitride film from the parentsubstrate.
 2. The method as recited in claim 1, wherein the parentsubstrate is selected from one of sapphire (Al₂O₃), spinet (MgAl₂O₄) orsilicon carbide (SiC).
 3. The method as recited in claim 1, wherein thesingle crystalline nitride film is formed by a hydride vapor phaseepitaxy.
 4. The method as recited in claim 1, wherein the step b)comprises the steps of: a1) positioning a material selected from a groupIII at a first temperature region of 600° C. to 900° C. in the reactingchamber and positioning the parent substrate at a second temperatureregion of 1000° C. to 1100° C. in the reacting chamber; a2) injecting anitrogen gas into the reacting chamber; a3) injecting a hydrochloricacid gas into the reacting chamber; and a4) injecting an ammonia gasinto the reacting chamber.
 5. The method as recited in claim 1, whereinthe parent substrate is heated up to 600° C. to 1000° C.
 6. The methodas recited in claim 1, wherein the an exhausting chamber is positionedbetween the reacting chamber and the heating chamber, and wherein thereacting, exhausting and heating chambers are isolated are from eachother by shutters.